1. Field of the Invention
The present invention relates to a curtain coating apparatus and method, and more particularly to an apparatus and method for coating a continuously-running support (hereinafter referred to as a "web") with a variety of liquid compositions in a curtain coating method for use in the manufacture of photosensitive material film, photographic printing paper, magnetic recording tapes, information recording paper such as pressure sensitive paper and heat sensitive paper, presensitized offset plates, adhesive tapes, or the like.
2. Description of Related Art
In the curtain coating method, a curtain of coating liquid, free-falling from a coating hopper, impinges on a continuously-running web so that the web can be coated with the coating liquid. Since the curtain coating method prevents small bubbles from accompanying the web between the web and the coating liquid, the web can be coated at a high speed. In the curtain coating method, it is important to coat the web with the coating liquid at the uniform thickness from the beginning of coating in order to prevent a transport roll from becoming unclean due to the unsatisfactory drying of the thickly-coated part of the web and achieve the satisfactory coated surface.
To achieve this object, U.S. Pat. No. 3,508,947 discloses a method in which a rotatable or slidable deflector, which is provided on the route of the free-falling curtain of the coating liquid, is moved back from the route at the start of the coating. Until a stable curtain with a desired amount of liquid is formed at the start of the coating, the deflector is arranged in such a way as to block the curtain of the coating liquid. The blocked coating liquid flows down on the deflector and is received by a container. After the conditions for the stable curtain are met, the deflector is rotated or slid and is moved back from the flow-down route of the curtain. Consequently, the curtain is applied on the web.
In the coating method using the deflector, a pool of the coating liquid is formed at the upstream of the collision point where the curtain impinges on the deflector. When the deflector is moved back to start coating, the pool of the coating liquid is applied on the web and a thickly-coated part is formed on the web. It causes the transport roll to become unclean due to unsatisfactory drying. Moreover, bubbles are easily involved in a coating bead part when the curtain is applied to the web. This results in inclusion of bubbles in the coated liquid and the streaks and unevenness of the coated surface. Therefore, the coated surface cannot be uniform. In particular, the pool of the coating liquid falls onto the web, and this results in a pool of the coating liquid (commonly called "heel") at the upstream of the contact line between the web and the curtain. Bubbles are easily involved in the heel.
To address these problems, U.S. Pat. No. 4,851,268 discloses a deflector having a plurality of lips at the end thereof; Japanese Patent Provisional Publication No. 4-61951 discloses a deflector having a doglegged lip at the end thereof; Japanese Patent Provisional Publication No. 2-277570 discloses an deflector that is made of hydrophobic material; and Japanese Patent Provisional Publication No. 8-89886 discloses a method of starting the coating with a small amount of coating liquid and then immediately increasing the amount of the supplied coating liquid.
The deflectors disclosed by U.S. Pat. No. 4,851,268, Japanese Patent Provisional Publication No. 4-61951 and Japanese Patent Provisional Publication No. 2-277570 cannot prevent the web from being thickly coated or prevent the bubbles from being involved in the coating liquid if the coating is performed at a high speed. Thus, the uniform coating film cannot be formed on the surface of the web.
The method of Japanese Patent Provisional Publication No. 8-89886 cannot solve the problem in which the bubbles are involved in the coating liquid just after the coating. Moreover, the web cannot be coated uniformly since the bubbles are involved in the coating liquid due to a rapid increase in the amount of the supplied coating liquid.
This problem occurs not only at the start of the coating but at the end of the coating, but no measure has been taken at the end of the coating.